How Fast Can You Send?

Choose the most powerful server that you can afford. If speed is a factor, a more powerful server will deliver your messages faster. If budget is limited, a less powerful server may still get your message out in an acceptable time frame.

Sending Rate
The sustained rate at which you can send email messages is based on many factors:
  1. Shared vs. Dedicated
  2. Dedicated Server performance level
  3. Email Marketing Program used
  4. Use of SMTP Pipelining
  5. Use of SSL
  6. Proper use of Concurrent connections
  7. Network speed between you and us
  8. Message size
  9. Recipient server and DNS performance
  10. Blacklisting and Greylisting
  11. Recipients/message
  12. Processing
Maximum Rate
The "maximum sending rate" (msgs/hr) is a theoretical maximum rate that you can get through the service. It assumes optimal sending conditions: very small (1 KB) messages, through a very fast network connection, all to the same recipient domain, where there is no blacklisting or greylisting, where SMTP Pipelining is used without SSL, and where the recommended number of concurrent SMTP connections is employed.
Spotlight Mailer Maximum Rate
The "maximum sending rate" (msgs/hr) for Spotlight Mailer is a theoretical maximum rate that messages can be sent from Spotlight Mailer under the same optimal sending conditions: very small (1 KB) messages, all to the same recipient domain, where there is no blacklisting or greylisting, and where SSL is not used. Spotlight mailer is has an extremely fast connection to the SMTP server, uses SMTP Pipelining, and uses 4 concurrent connections.

Actual throughput with Spotlight Mailer will be less based on the other factors which affect sending rate: SSL, Message size, Recipient server and DNS performance, blacklisting and greylisting, and any additional processing being performed (e.g. anonymization or encryption).

Expected Rate
Under realistic sending conditions, you may find your sending rate to be closer to the listed "Expected" rates, assuming that you also use SMTP Pipelining, 1 recipient per message, no SSL, have moderately small messages, use a good email sending program, and use the recommended number of concurrent SMTP connections.
Expected Daily Rate
This is an estimate of the number of messages that you could send in 24 hours of sustained sending at approximately the "Expected" hourly rate.

Sustained vs Burst Rate

For some customers, the speed of sending is very important. There are two significant modes of sending:

Sustained Rate
Sending at a consistent rate for a long period of time. E.g. 20,000 messages/hour for minutes or hours. Sustained rates are relevant when sending an email marketing blast to a large subscriber list.
Burst Rate
A "burst" refers to sending a bunch of messages in a very short time; e.g. 25 or 50 messages within a second or two. Burst differs from "sustained" in that when you are not "bursting" you are sending one or a few messages here and there ... infrequent sending. Bursting is relevant for transactional email messages when you are sending them "as needed" but require the ability to send many at once should that need arise, as it will.

Sending speed is important for customers who need to send large mailings at a sustained rate. Understanding sending speed helps you determine how long it will take to send that blast to 100,000 subscribers.

Factors Affecting your Sustained Sending Rate

There is a theoretical maximum number of messages/hour that any server can manage. How fast you can actually send is affected by a number of factors.

1. Shared vs Dedicated
Dedicated servers will generally be faster. On shared servers, you must share the server sending capacity with others and thus you do not have control over the capacity available to you at any particular time.
2. Dedicated Server Performance Level
More powerful dedicated servers can handle more concurrent connections and thus give you higher sending rates.
3. Email Marketing Program
Different email marketing programs have different capacities for how efficiently they can send bulk email. Simply switching from one program to another can increase your throughput significantly.

LuxSci Spotlight Mailer is a very efficient program.

4. SMTP Pipelining
Use an email marketing program (like LuxSci Spotlight Mailer) that supports SMTP Pipelining. With this feature, the program opens a single authenticated connection to the server and sends multiple messages in succession over that connection. This is significantly faster than opening a new connection and logging in again for every single message to be sent.

LuxSci Spotlight Mailer uses SMTP Pipelining.

5. Use of SSL
SSL is extremely useful for security and for the protection of your username, passwords, and message content. However, when using SSL, your email marketing program and your server must perform work encrypting and decrypting all of your messages. This overhead will slow down your rate of sending.

LuxSci Spotlight Mailer does not use SSL by default as the connections are between LuxSci servers behind LuxSci's firewalls. SSL is not needed in this case.

6. Concurrent Connections
If your program can open 2 connections to our SMTP servers at the same time and send two messages at once, then your sending rate can generally be twice as fast. Depending on how powerful your server is and how slow your network connections are, you can use more and more concurrent connections to achieve higher and higher sending rates. Combined with SMTP Pipelining, an appropriate number of concurrent connections goes a long way to maximizing your throughput potential.

The recommended number of concurrent connections for best results in sustained sending are given for each server type on the Pricing page.

Note, however, that if you use more concurrent connections that is recommended, then you are likely just over-working your server. That results in your sending rates actually getting slower. Stick to the recommended number of concurrent connections.

LuxSci Spotlight Mailer uses 4 concurrent connections for all customers - dedicated or shared. However, due to the lack of network speed issues slowing down each Spotlight Mailer connection, this behaves effectively like 8 concurrent connections.

7. Network Speed
Your messages must be transmitted from your email marketing program to our servers. The speed of your network and the distance between your sending computer and our servers can significantly impact the maximum rate that you can send messages.

For example, LuxSci Spotlight Mailer sends from a server right next to your outbound email servers and thus network speed is not a factor. For someone connecting from outside of LuxSci or internationally, the speed can slow down significantly.

8. Message Size
Like network speed, the larger your messages are, the more time it will take to transmit them from your email marketing program to our servers. For example, on a fast network, increasing message size from 1KB to 1MB decreased throughput by 50%. The actual impact of size on you will depend greatly on your network speed and other factors.
9. Recipient Email Server and DNS Speed
In order for our servers to deliver messages to your recipients, they have to (a) look up where to deliver the messages to (DNS), and (b) talk to those servers to deliver the messages to them. If the DNS lookup as slow or the recipients are in domains that no longer exist, this step can be slow. If the recipient email serves are overloaded, have a slow network, or are having other issues, then the delivery phase can be slow. Delivering many messages to recipients with these issues will slow down your entire sending process... as other messages have to wait for these to be sent.

You can get around this recipient slowness issue by using our "Anonymous SMTP" ports (587, 6025, and 6465). In this case your messages are immediately queued on our servers and delivered "later". This does not speed up the actual time to when the recipients get the messages (it will in fact slow that down); however, it will speed up the rate that your email marketing program delivers those messages to our servers.

10. Blacklisting and Greylisting
If your email content or sending patterns have gotten your server blacklisted or greylisted, then delivering email messages to recipient servers that are now blocking you or deferring you can slow down your delivery rates.
11. Recipients per message
Most email marketing programs send a separate message to each recipient. This allows them to track opens, views, etc. However, if you send each message to many recipients (e.g. 100s of recipients), then your sending program has significantly fewer messages to deliver to our servers and this process can happen 10s or 100s of times faster than if you sent in the usual one recipient/message pattern.

Additionally, if each message contains only recipients in a specific domain, then actual delivery to these recipients will be expedited by this efficiency. E.g. If you are sending to 500 AOL users, instead of sending 500 individual messages, send one message with all 500 AOL users listed as "BCC" recipients. Delivery will be almost 500 times faster.

12. Outbound Processing
If you are using SMTP Anonymization, or if you are using email processing features that come with Premium High Volume (e.g. content scanning, recipient restrictions, SecureLine email encryption, etc.) then the messages will be queued and processed and then sent on to their recipients as appropriate. These steps will slow down message delivery.

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